The present invention relates generally to matching sensors, and more particularly to compensating the output of one sensor in real time to accurately match the output of another sensor.
Sensors include sensors with analog outputs and sensors with digital outputs. Sensors measure physical quantities and include conventional displacement, velocity, acceleration, force, and pressure sensors. Pressure sensors include pressure transducers such as microphones. Certain applications, such as the evaluation of acoustic particle velocity through a pressure gradient measurement, require using two microphones having outputs which are accurately matched in amplitude and phase. Inexpensive microphones costing a few dollars do not have the amplitude and phase of their outputs accurately matched to each other, or to a reference microphone, due to manufacturing tolerances or design differences. Such inexpensive microphones are not suitable for precise measurement applications. It is known to use an expensive pair of matched microphones, costing several thousands of dollars, for precise applications. It is also known (U.S. Pat. No. 5,125,260) to use a computer to store measured phase and amplitude frequency responses of two unmatched microphones, to apply curve fits to such responses to extract phase and amplitude correction coefficients for each microphone, to store the amplitude and phase correction coefficients in an independent computer data base, and to later use such amplitude and phase correction coefficients to computationally compensate the unmatched microphone pair for phase and amplitude mismatch. Such known sensor output compensation technique operates in the frequency domain and does not operate in real time (i.e., such technique does not automatically compensate the unmatched outputs of the microphone pair at the instant the pair is sensing acoustic pressure). What is needed is a relatively inexpensive technique to accurately match the outputs of unmatched sensors in real time.